Self-metering reservoir

ABSTRACT

A bubbler container assembly particularly adapted for use in vapor generating systems comprising a main outer vessel, an inner bubbler vessel, a carrier gas inlet and a vapor outlet such that the inner bubbler vessel is contained within the main outer vessel and the bubbler container assembly is constructed so as to self-meter an incoming supply of vaporizable liquid during the introduction of a carrier gas and extraction of resulting vapor. Preferably, the system further provides for magnetic induced centering and positioning of the inner buoyant bubbler vessel, fluid temperature sensing and control, connection of a fluid makeup supply, carrier gas inlet supply, and vapor extraction outlet.

This is a division of application Ser. No. 08/799,746, filed Feb. 12,1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems for maintaining agenerally constant level of fluid within a vessel and more particularlyto systems for supplying vapor to a chemical process by introducing acarrier gas into a fluid column of vaporizable liquid.

2. Background Information

A common technique used in vapor generating systems for deliveringchemical vapor to a process chamber is to force a carrier gas bubblethrough a chemical fluid in a bubbler and then to deliver the resultingvapor from the bubbler to the process chamber. Traditional bubblers,including those utilized in presently available automatic refillsystems, rely on relatively large fluid volumes to intrinsicallycompensate for deviations in fluid level which can negatively effect theresulting vapor concentration. Since vapor sources in the fiber opticsand semiconductor industries are often hazardous fluids, there has beenan increasing focus on the occupational safety and health concernsresulting from use of such fluids. This has resulted in reducing themaximum allowable volumes of many of these fluids within the work place.It is therefore desirable to reduce the required fluid volume at thepoint of vapor generation without compromising vapor concentrationcontrol.

Typically a bubbler container is comprised of a single vessel whichholds an expendable volume of vaporizable fluid. A carrier gas such ashydrogen, helium or nitrogen is introduced at the lower level of a fluidcolumn, travels up through, and exits the fluid surface into a headspace. As the carrier gas passes through the fluid column it becomesentrained with vapor which results in a corresponding reduction of thefluid volume. This reduction of the fluid level in the bubbler containermay be significant for several reasons. For example, the vaporizationefficiency and overall vapor concentration uniformity are both affectedby the fluid level and are both important elements which may affect thestrict tolerance requirements of the process application. In addition,the physical fluid column in the bubbler not only determines the carriergas contact time and resulting bubble geometry but also represents themass to which thermal energy is either added or extracted. It alsodefines the head space present above and within the bubbler containerwhich has been found to negatively effect the vapor concentration andultimate bubbler performance when not optimized.

Inasmuch as vapor extraction from a fluid volume results in depletingthe fluid volume of a bubbler, causing variations in vaporconcentration, a means of replenishing this fluid is desirable. Somemethods include manually replacing the bubbler ampule once the volume offluid reaches a predetermined minimum acceptable level. Other manualmethods rely on an auxiliary supply of fluid to replenish the bubblerduring intermittent periods of non-use. Although such methods can resultin reducing many of the concerns associated with prior art expendablebubblers, such as reducing the risk of contamination during ampulereplacement or any necessary fluid replenishment, these systemstypically remain idle until an interruption in vapor extraction providesa refill opportunity. With many of the advanced processes running forlong periods of time before a refill opportunity is presented, the fluidlevel may descend considerably resulting in less than optimum vapordelivery efficiency. Although there are techniques which can be employedto compensate for the influences of a constantly descending fluidvolume, such as intermittent refill in between process runs, suchtechniques can be complex and costly. In any event, such techniques donot satisfy the level of control achieved by the present invention.

In addition to manual replenishment of fluid, automatic bubbler refillsystems are also available. However, such systems typically employ floatcoupled electronic devices, such as level controllers, to control thereplenishment of fluid in the bubbler. Such devices are prone to failureand are generally the most common failure mechanism in the system. Othertypes of fluid level sensors such as optical, load cell monitoring ofthe contents, and resistance probes have been employed. However, the useof such devices can be costly, prone to error, and with many of thefluids being flammable, represent ignition sources if not properly ratedand maintained.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide a costefficient and reliable bubbler reservoir system capable of metering anexternal supply of fluid into itself to maintain a nearly constantliquid level while it bubbles vapor to a process.

Another object is to restrict an incoming supply of fluid to the bubblerto prevent overfill conditions without the need for electronic oroptical level detection devices.

A further object of the invention is to provide a means of dramaticallyreducing the fluid volume at the point of vapor generation withoutcompromising vapor concentration control.

Another object of the present invention is to prevent or reduce weareffects or particle generation from friction by the use of magneticforces.

A further object of the invention is to provide an optimum mechanism forcontrolling the temperature of the inner bubbler fluid by directingmakeup fluid along the outer walls of the inner bubbler vessel wherethermal energy can be added or extracted, as required, prior tointroducing this fluid into the inner vessel, thereby reducing potentialfor thermal cycling as makeup fluid mixes with inner bubbler fluid.

Another object of the invention is to provide a means of calibrating thebuoyant interaction of the inner bubbler vessel relative to differentfluid applications and more specifically to differences in specificgravity through the use of opposing magnetic fields, one fixed withinthe inner buoyant bubbler vessel and one which can be adjusted at thebase of the outer vessel.

The above and other objects of the present invention are accomplished ina system that overcomes the disadvantages and limitations of the priorart by providing an apparatus and method to generate and support thedelivery of vapor from a vaporizable source contained in a bubbler asdescribed herein and to support the real-time metering of an incomingsupply of makeup fluid to replace fluid lost as a result of theconsumption of vapor. The system meters the introduction of the incomingfluid in direct response to the extraction of fluid being converted toand carried off as vapor. The invention's novel approach to minimizingthe resident fluid volume required to support the continuous delivery ofvapor is most notably due to its intrinsic control of makeup fluid indirect response to small changes in fluid within the bubbler. In apreferred form, the invention may also include one or more of thefollowing: the use of adjustable magnetic fields to compensate forfluids of different specific gravities, the use of magnetic fields toreduce the possibility of particulate contamination otherwise resultingfrom surface abrasion at the contact points of moving parts within thebubbler, the use of thermoelectric converters to control the temperatureof the bubbler fluid, a reduction in the overall bubbler size andtemperature control type, and the ability to integrate the device muchcloser to the process site. The latter features not only reduce thefinal cost of the bubbler, and its integration into process equipment,but also further reduces the degrading influence of ambient temperatureeffects associated with longer vapor delivery lines running from abubbler to the point of process.

The present invention is also particularly advantageous in applicationswhere a plurality of bubblers are supported by a single bulk refillsystem. In a typical bulk refill system, a call for makeup fluid occurswhen there is a discontinuation of a process due to the detection of alow liquid level in the bubbler. Due to the potential for multiple priorart bubblers to call for material at the same time, the bulk refillsystem must be adequately sized for the total volume consumption rate ofthe plurality of bubblers. With the present invention, there is nocommunication required between the process and the bulk refill system.Since a plurality of bubblers can be refilled in real time, there isalso a substantially reduced demand on the bulk refill systems. Further,there is no discontinuation of process required; nor is there arequirement for venting the bubbler as it is refilled. Refill occurs ata volume flow rate equivalent to the extraction rate of vapor from thebubbler. This creates an optimum condition for the bulk distributionsystem in that fluid is only required at the rate of consumption at anyone or more points actively delivering vapor. This feature is incontrast to manual vapor delivery systems in which fluids arereplenished during periods of time when vapor is not being deliveredfrom the bubbler. In prior art automatic refill systems, the supportingvolume flow rate demand is a function of how often a makeup opportunityis presented and the volume of fluid necessary to refill any probablenumber of supported bubblers at any period in time. In both cases, thedistribution system must be sized for the maximum volume makeup flowrate of the plurality of bubblers supported by the system. This methodresults in placing a volume flow rate demand on the refill system equalto the total volume of makeup fluid required by the plurality ofbubblers. In contrast, the present invention calls for makeup fluid whenit is actively delivering vapor, the maximum volume flow rate of therefill system is a function of the total flow-rate consumption of liquidtimes the number of bubblers in an active vapor delivery state. Thus,there is a significant benefit on both the initial cost and safety ofthe bulk refill system because the sizing of the system components canbe significantly reduced as well as the total volume of hazardous fluidwithin the delivery system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front face cutaway illustration of a bubbler containerassembly in accordance with the present invention.

FIG. 2 is an isometric cutaway illustration of the bubbler containerassembly.

FIG. 3 is a diagrammatic illustration of a bubbler container assemblydepicted within a basic operational control scheme for implementing thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best presently contemplated modes ofcarrying out the invention. This description is not to be taken in alimiting sense but is made merely for the purpose of describing theprinciples of the invention.

The description herein presented refers to the accompanying drawings inwhich like reference numerals refer to like parts throughout the severalviews. FIG. 1 is an illustration depicting an assembly of elementscomprising the bubbler. During operation, the bubbler assembly operatesas a float coupled metering device which supports the generation ofvapor from a vaporizable fluid contained within the float vessel. Amongthe major elements depicted in FIG. 1 are the primary containment vesselS and the inner bubbler float vessel 6. A carrier gas, supplied andcontrolled externally, connects to port 2 through fitting 24, travelsthrough the conduit 8 and exits into the lower level of the vaporizablefluid present within the inner float vessel 6. As the carrier gastravels up through the fluid it becomes entrained with vapor, exits thefluid surface into the head space 20 and exits discharge port 3 throughfitting 25. As a result of vapor generation, the fluid level of theinner float vessel 6 descends. This action results in reducing theweight of the inner float vessel 6 which is otherwise suspended withinthe fluid of the outer vessel 5. As a function of weight loss, the innerfloat vessel 6 gains buoyancy and ascends within the makeup fluidchamber 22 of the outer vessel S. The upward buoyant movement of theinner vessel 6 withdraws metering stem tip 10 from aperture 10a which isshown in FIG. 2. This action meters a corresponding makeup fluid flowinto the makeup fluid chamber 22 from an externally supplied sourceconnected to port 1 and fitting 23. As the makeup fluid level riseswithin the makeup fluid chamber 22 of outer vessel 5, the inner floatvessel 6 continues to travel upward. In the preferred embodiments shownin FIG. 1 and FIG. 2, the magnets 14 are encased by fittings 15 in eachof the four corners of the upper portion of the outer vessel 5. Therising inner float vessel 6 is increasingly repelled by the flux fieldsof magnet 16 as it ascends into the flux fields of magnets 14. At apoint when the repelling force exceeds the buoyant lift of the innerfloat vessel 6, makeup fluid in the outer vessel 5 reaches and cascadesinto the inner float vessel 6 through holes 9. The introduction ofmakeup fluid into the inner float vessel 6 increases its weight causingit and metering tip 10 to descend into aperture 10a restricting themakeup flow rate.

During operation, the extraction of fluid from the inner float vessel 6by means of evaporation results in lowering the energy level of thefluid volume. This thermal energy loss is a function of the latent heatof vaporization for the fluid being evaporated and the extraction rateof fluid per unit time. The fluid temperature within the bubbler may becontrolled and monitored by standard industrial thermoelectrictemperature control modules 27, such as that sold by Melcor Corporationas part number CP1.0-127-051-2 and a thermal well 7 filled with oil andincorporating a temperature sensing thermocouple, such as that sold bySimpson as Type 21244, Sensor Type RTD. The thermoelectric temperaturecontrol module power leads 29 and temperature probe sensor leads 4integrate by means of standard industrial practice to a programmabletemperature controller 32, shown in FIG. 3. Aluminum plates 26 fastenedto the exterior walls of the outer vessel 5 increase the thermalexchange rate between the thermoelectric converters 27 and the fluidvolume in the outer vessel S. Commercially available convection typeheat transfer fins 28, such as those sold by Melcor Corporation, areplaced on the outer faces of the thermoelectric converters 27 toincrease the thermal exchange rate efficiency of the temperature controlunit. These elements are incorporated so as to provide ampule thermalcapacity as dictated by the amount of fluid to be evaporated per unittime and the fluid's latent heat of vaporization.

The dry weight of the inner vessel 6 is compensated for by the repellingforces of the opposing fields of the inner vessel disc magnet 11 and theouter vessel ring magnet 12. Because the invention is intended to beutilized with many different fluid types, compensating for fluidcharacteristics such as specific gravity and viscosity is accomplishedby setting the distance between the outer vessel ring magnet 12 and theinner vessel disc magnet 11. This adjustment is accomplished by turningthe outer vessel magnet backup ring 13 which is threaded into the baseof the outer vessel 5. In function, an otherwise dry inner vessel 6 isdynamically suspended just above its fully seated position within theouter vessel metering aperture 10a. This results in reducing the meteredinflux of a makeup fluid entering the outer vessel to a point less thanthe lowest possible evaporation rate during the introduction of acarrier gas. Isolation valves incorporated within the supply stream ofthe fluid makeup, carrier gas inlet, and vapor delivery lines work as agroup and are either open or closed as a group thereby totally isolatingthe invention when vapor is not needed.

Optimum functionality of the preferred embodiments are dependent uponthe strength of the magnetic fields. For this reason, rare earth magnetssuch as the type sold by Master Magnetics, Inc. as Samarium Cobalt arepreferred to satisfy the various shapes noted as magnets 11, 12, 14, and16. Because the invention is intended to handle fluids that must becontamination free and specifically free of byproducts resulting from areaction between the fluid and the magnetic material, magnets 11 and 16should be fully encased in the same material as that of the inner andouter bubbler vessels.

FIG. 3 depicts a diagrammatic illustration of the vapor generationsystem. Representative are the reservoir fluid level 30, and innerbubbler vessel fluid level 31, as a carrier gas is introduced throughconduit 2, exits into and travels up through the inner vessel bubblerfluid contained therein and is converted to a vapor state. This actionreduces the amount of fluid contained within the inner bubbler vessel 6.The resulting loss of fluid within the inner bubbler vessel 6, as fluidis converted to vapor, reduces its total weight resulting in an increasein buoyancy; the total dry mass of the inner vessel 6 in conjunctionwith a preferred minimum volume of fluid therein result in a fullyseated state with respect to the position of the metering stem tip 10and the fluid makeup aperture 10a. Although absolute isolation of makeupfluid being introduced into the reservoir is not intended, in the fullyseated state, the influx rate of makeup fluid is far below the lowestpossible liquid to vapor conversion rate under any normal state ofoperation. To insure that the reservoir cannot become overfilled withfluid, independent isolation of the fluid makeup source through port Iand the carrier gas source through port 2 is included. As seen in FIG.3, representative industrial standard valves, such as that sold byNupro-Swagelok, Co. as part number SS-BNV51-C are used for positiveisolation of the inlet ports 1 and 2, and outlet port 3. In thepreferred embodiments, all three valves, 34, 35, and 36, are of thenormally closed automatic type. As represented in FIG. 3, controlsignals to each of the valves would originate from a control system 33.This control system would most likely be part of the overall processautomation platform controlling all the devices necessary to support thevapor deposition application.

It should be understood that the embodiments described herein merelyillustrate principles of the invention in selected preferred forms. Manymodifications, additions and deletions may, of course, be made theretowithout departure from the spirit and scope of the invention as setforth in the following claims.

What is claimed is:
 1. An apparatus for reducing friction between twovessels comprising:an outer vessel having an inner chamber, an innervessel disposed within said chamber, a first inner vessel magnetdisposed at one end of said inner vessel and proximate to at least onefirst outer vessel magnet having an opposing magnetic field, a secondinner vessel magnet disposed at an opposite end of said first innervessel magnet, a plurality of second outer vessel magnets positioned inproximity to and having opposing magnetic fields to said second innervessel magnet whereby opposing magnetic fields of said inner and outermagnets are employed to maintain concentric suspension of said innervessel.
 2. The apparatus according to claim 1 wherein a distance betweensaid first inner vessel magnet and said first outer vessel magnet may beadjusted to compensate for different weights of fluids to be containedwithin said vessels.
 3. The apparatus according to claim 2 wherein saidfirst outer vessel magnet is a ring magnet.
 4. The apparatus accordingto claim 3 wherein said first inner vessel magnet is a disk magnet. 5.The apparatus according to claim 2 wherein said second inner vesselmagnet is centered within the flux fields of said plurality of secondouter vessel magnets.